1. Field of the Invention
The present invention relates to a method of manufacturing a metal foil laminated plate comprising the step of forming and sticking a resin porous layer on to a metal foil having a conductive bump and to a metal foil laminated plate obtained by the manufacturing method and is useful for a technique for conductively connecting the wiring layers of a multiplayer wiring board.
2. Description of the Related Art
In recent years, an increase in the density of a wiring board has been required with a reduction in the size and weight of electronic equipment. Correspondingly, the multilayer structure of a wiring layer has been enhanced. As such a structure of the multilayer wiring board, generally, an insulating layer and a wiring layer having a pattern formed thereon are sequentially laminated and the wiring layer is conductively connected through an inner via hole. As the conductive connecting method, there have been known a method of plating the inner peripheral surface of a via hole, a method of plating the internal space of the via hole to form a metal column, a method of filling a conductive paste in the internal space of the via hole, and the like.
As disclosed in Japanese Patent Application Laid-Open No. 6-268345, particularly, attention has been paid, in respect of the reliability of an inter layer connection, to a method comprising the steps of forming a through hole on a prepreg having a releasing film on at least one of surfaces of a prepreg base material, filling a conductive paste in the through hole, separating the releasing film, laminating a metal foil on a surface from which the releasing film is separated, and heating and pressurizing to form the laminated product.
In the method of carrying out metal plating or filling a conductive paste after the formation of the via hole, however, there is a tendency that a laser processing is required or the steps are complicated.
On the other hand, there has been known a technique for utilizing a resin porous film as the insulating layer of a multilayer wiring board in order to reduce a dielectric constant. Moreover, there has been known a prepreg for a wiring board impregnated with the half cured thermosetting resin in the hole of the resin porous film. In such cases, however, a connecting structure for conductively connecting wiring layers is formed separately from the formation of the resin porous layer.
Therefore, it is an object of the present invention to provide a method of manufacturing a metal foil laminated plate in which opening the via holes is not required and a connecting structure for conductively connecting wiring layers is obtained at a simple step and a metal foil laminated plate which is obtained by the manufacturing method.
The object can be attained by the present invention in the following manner.
More specifically, the present invention provides a method of manufacturing a metal foil laminated plate comprising the step of forming and attaching a resin porous layer onto a metal foil by a wet coagulating method, wherein a metal foil including a conductive bump having an almost equal height on a film forming side surface is used. According to the manufacturing method of the present invention, a metal foil including a conductive bump having an almost equal height on a film forming side surface is used as a metal foil for forming and attaching a resin porous film by a wet coagulating method. Therefore, it is possible to form the conductive connecting structure for wiring layers simultaneously with the formation of the resin porous layer. Accordingly, the hole-opening step is not required and a connecting structure for conductively connecting the wiring layers can be obtained at a simple step.
It is preferable that an amount of application of a film forming solution should be regulated such that the height of the surface of a resin porous layer after the film formation is almost equal to that of the conductive bump. In this case, the conductive bump can be easily exposed to a surface, and furthermore, the resin porous layer can be prevented from being lower than the conductive bump to generate concavo-convex portions.
On the other hand, the present invention provides a metal foil laminated plate comprising a metal foil including a conductive bump having an almost equal height and a resin porous layer laminated integrally, the conductive bump being exposed. According to the metal foil laminated plate of the present invention, the wiring layers can be conductively connected by the conductive bump, and furthermore, the resin porous layer has the function of insulating the wiring layers. Moreover, it is possible to reduce a dielectric constant and a dielectric loss by the resin porous layer.
Further, another metal foil laminated plate of the present invention provides a metal foil laminated plate comprising a metal foil including a conductive bump having an almost equal height, a resin porous layer laminated integrally, and a thermosetting resin impregnated in a hole of the resin porous layer, the conductive bump being exposed from the resin porous layer.
According to another metal foil laminated plate of the present invention, the wiring layers can be conductively connected by the conductive bump. In addition, the metal foil laminated plate according to the present invention can be sequentially bonded and laminated by a thermosetting resin impregnated in the hole of the resin porous layer. Consequently, it is possible to easily manufacture a multilayer wiring board.